Conventional magnetic sensor devices exist that are composed of a substrate, on which a magnetoresistance effect element (magnetoresistive element) is formed, and a magnet for applying a bias magnetic field to the magnetoresistance effect element (for example, see Patent Literatures 1 and 2). Patent Literature 1 discloses a magnetic sensor device in which position of a permanent magnet is adjusted such that a bias magnetic field strength of a magnetosensitive direction of a ferromagnetic thin film magnetoresistive element becomes a magnetic flux amount less than or equal to a saturation magnetic field. Patent Literature 2 discloses arrangement of two magnetoresistance effect elements on a substrate, disposal of the magnetoresistance effect elements and the substrate within a body case, and disposal of a permanent magnet on the backside face of the body case.
Moreover, among conventional magnetic sensor devices, there exist magnetic sensor devices in which the magnetoresistance effect element is formed upon a magnetic material carrier, and a bias magnet and the magnetic material carrier oppose one another and sandwich a conveyance path of the object to be detected (for example, see Patent Literature 3). Among conventional magnetic sensor devices, there exist magnetic sensor devices that use a single detector to detect both a soft magnetic material included in the object to be detected and a hard magnetic material included in the object to be detected (for example, see Patent Literature 4).